Available online a t www.scholarsresearchlibrary.com Scholars Research Library Archives of Physics Research, 2010, 1 (3):89-110 (http://scholarsresearchlibrary.com/archive.html) ISSN 0976-0970 CODEN (USA): APRRC7 Astrophysical relevance of Strange Quarks Navjot Hothi† and Shuchi Bisht * Department of Physics, Kumaun University, Nainital, Uttrakhand, India ______________________________________________________________________________ ABSTRACT In this contribution, peculiarities in the nature of strange quarks in relevance to astrophysics are investigated. The absolute stability of strange quark matter is a viable possibility and immensely affects physics at the astrophysical scale. Relativistic heavy-ion reactions offer a stage to produce this exotic state of matter and we have discussed the enhanced production of strange particles during these reactions within the framework of quark-gluon plasma (QGP) along with its observable implications. The role of strangeness for compact star phenomenology is explored. Emphasis is laid upon the possibility of existence of a third family of strange quark stars and its study help in revealing a number of unexplored features of the cosmos. Bag model parameters have been used to determine some integral parameters for a sequence of strange stars with crust and strange dwarfs constructed out of strange quark matter crust. A comparative analysis is performed between the strange and neutron stars and the strange and white dwarfs based upon these intrinsic parameters and paramount differences are observed. PACS numbers: 12.38.Mh, 25.75.Nq, 14.65.-q, 97.60.Jd, 26.60.-c Keywords: strangeness, strange stars, quark-gluon plasma, deconfinement. ______________________________________________________________________________ INTRODUCTION The last few years witnessed the inclusion of strangeness as another degree of freedom in astrophysical systems. The intriguing strange quarks have far reaching implications on certain unexplored features of the cosmos and could unravel some mysteries of the Universe. Strangeness walks hand in hand as an interrogatory feature right from the birth of the Universe that is from big bang to the end of stellar evolution. The astrophysical domain of strange quarks spans over the existence of a stable hypothetical state of matter called strange quark matter to the possible existence of strange stars and it also serves as an evident signature for the presence of QGP. In this paper, we will outline some recent developments in the study of matter with strangeness under extreme conditions with relevance to astrophysics and will discuss features that are leading to the rapid growth of this field, both on theoretical as well as experimental fronts. 89 Scholar Research Library Shuchi Bisht et al Arch. Phy. Res., 2010, 1 (3):89-110 ______________________________________________________________________________ The intimacy between astrophysics and strange quarks depends strongly upon the strange quark matter hypothesis. It states that for a collection of more than a few hundred u, d and s quarks, the energy per baryon E/A of strange quark matter (SQM) can be well below the energy per baryon of the most stable atomic nuclei (such as iron or nickel). Thus, everything which we see around us is in the metastable state and if conditions for the creation of net strangeness are met, the matter would not make back to ordinary hadrons. The physics of SQM can have an intimate relationship with the QGP state and we could study deconfinement at low temperatures. The ultra-relativistic heavy-ion collisions aim at creating mini Big-Bang in the laboratory and an enhanced production of strange particles during these collisions provide evident signatures for the presence of QGP and help in developing a connection between Astrophysics and Heavy-Ion Physics. Thus, the heavy ion reactions exhibit replicas of the situation created during the birth of the universe and enable physicists to study the behaviour and properties of big-bang matter in laboratory and help in studying how the elementary properties of matter change in deconfined vacuum state. There is a possibility of existence of hyperstars, compact stars composed of strongly attractive hyperonic matter connected to strange hadronic matter and MEMOs (hypernuclei containing strange baryons). The presence of hyperstars relies solely upon the assumption of existence of SQM. Physicists [1,2] are looking forward for a possible existence of these new class of compact stars completely made up of SQM, which are called strange stars. There are indications that some earlier detected neutron stars could be strange stars or in fact could carry strangeness in the interior [3]. In this paper we have determined some integral parameters of strange stars with crust and strange dwarfs by employing the bag model parameters of the equation of state of SQM to two different models. Series of tabulated data has been used to perform a comparison between the strange and the neutron stars and also between strange and white dwarfs. Discriminatory features amongst the above are projected out by plotting these integral parameters against each other and this helped us in distinguishing the strange astrophysical objects from their non- strange counterparts. In section 2, we have discussed the enhanced production of strange particles in heavy-ion reactions followed by section 3, where strangeness distillation is witnessed as a possible phenomenon for the production of strangelets. SQM and the consequences of its stability are discussed in section 4 and 5 respectively. Strange stars and their intrinsic features are studied in section 6. In section 7, we have modelled the strange star phenomenology using the bag model parameters. Section 8 deals with a brief introduction to Multiquark states, followed by conclusion in the last section. 2. Strange particles enhancement in heavy ion reactions:-Signature for the presence of QGP The only unambiguous way to detect the transient existence of a QGP in heavy ion reactions, is through the observation of experimentally produced exotic remnants, most evidently, the enhanced production of strange particles in heavy ion collision reactions [4]. The equation of state of hot and dense hadronic matter created in these collisions is characterized by means of a phase diagram between baryon density and temperature. Now, at some critical temperature, the non-strange baryon density eventually witnesses a phase transition to a deconfined QGP state. The net strangeness is incorporated as a new degree of freedom for the equation of state to be passed through the heavy ion collisions. 90 Scholar Research Library Shuchi Bisht et al Arch. Phy. Res., 2010, 1 (3):89-110 ______________________________________________________________________________ Strange particles are relatively easy to detect by the tracks left behind by their decay products because the strange particles are naturally radioactive and their decay mode is through weak interactions. The time scale of this mode is extremely long as compared to the nuclear collision time. With greatly differing reaction rates in the medium, hadrons with varying strangeness content decouple at different times from the evolving system. Today, the evidence for QGP at various accelerator centres is quite overwhelming, yet very debatable. However, there is unanimity among physicists about significantly enhanced production of strange particles as a consequence of formation of QGP. For enhanced strangeness production, the kinematic threshold energy in the case of QGP is relatively lower than in the case of hadron gas. In a QGP, strangeness production occurs through the following reaction. ; The required threshold energy is 2m s~300 MeV (bare mass of strange quark=150 MeV). The gluon fusion channel is a dominant one in which the gluons fuse together to produce quark-anti quark pairs in the plasma and thus the subsequent hadronzation process lead to the formation of relatively large number of composite particles containing one or more strange quarks [5]. The gluon fusion channel is not accessible in normal collisions among hadrons. The formation time of QGP lies between t=0.2-0.8 fm/c. It is the time required for the gluon gas to reach initial chemical equilibrium. Assuming chemical gluon equilibrium, strangeness production by gluon fusion sets in at that time. Thus after a very short equilibration time, the strangeness saturates the phase space in a baryon-rich environment. The equilibration time may actually be shorter than the duration of nuclear collision. In fact, given the short hadronic interaction scale, the lifespan of strangeness can be considered infinite. The strange quarks and anti quarks observed in heavy ion reactions are freshly cooked from the kinetic energy of the colliding nuclei unlike the up and the down quarks which are brought into reaction by the colliding nuclei. This feature is supported by the fact that the drag forces of flowing matter is to a large extent different for strange baryon and antibaryon pair. Also, it is evident that at the time of particle freeze out, there is a considerable transverse/ radial collective flow. Thereby, we can say that the strange baryons and antibaryons are not dragged along the confined matter. Rather they must have been formed in coalescence of flowing matter. Actually, it is a strange fact that the mass of the strange quark and antiquark is equivalent to the temperature or energy at which the nucleons (protons and neutrons) and other hadrons dissolve into quarks. The quark gluon plasma is produced at a temperature ≥200-300 MeV, with a surviving time scale ≥0.5fm/c and energy densities of about 3-4 GeV/fm 3[5]. At this stage, charmonia formation is suppressed and strangeness is enhanced. The chemical temperature of 3 SPS and RHIC [6,7] is T Chem =165-170 MeV (energy density of 1GeV/fm ) and we are aware that the mass of the strange quark is about m s=150 MeV. This mass shows small variation with respect to temperature. For example, a higher temperature would lead to an increase in mass. The mass of strange quark at temperature T=182 MeV is ms(T=182MeV)= 200MeV.